The invention relates to a mount for connecting two relatively-vibratable objects and, more particularly, an engine mount.
An engine mount having first and second resilient elements and a damper for the suppressing large relative movements is known from published German patent application DOS No. 26 18 333. It is intended for supporting an internal-combustion engine in a motor vehicle and is said to prevent the transmission of disturbing vibrations from the engine to the chassis.
Another engine mount is disclosed in published German patent application DOS No. 26 16 258. It is basically afflicted with the same difficulties and drawbacks as the design according to published German patent application DOS No. 26 18 333. Especially when there is pronounced rocking motion of the supported engine, disturbing throbbing vibrations are set up in the chassis, and these cannot be readily eliminated. Modification of the individual parts of such an engine mount would be required.
The vibrations introduced into the mount for an internal-combustion engine in a vehicle are of two different types.
The first type occurs in the frequency range above about 30 Hz and is produced by the engine itself. These vibrations have a very small amplitude of a few tenths of a millimeter but manifest themselves in the vehicle as annoying, throbbing vibrations. To prevent this, they should be isolated from the chassis to the extent possible.
The second type of vibrations occurs in a frequency range of up to about 12 Hz and is produced when the vehicle travels over a rough road. In extreme cases, these vibrations may shake the engine with amplitudes reaching as much as about 10 centimeters. In the case of a passenger-automobile engine, for example, such excursions are intolerable. Therefore, they must be suppressed.
This can be done with a damper, for example, a stiff spring between the engine and the relatively-immovable chassis. However, this dynamically stiffens the junction between engine and chassis or, in other words, hardens the engine mount. This impairs the isolating action of the mount and, hence, results in transmitting the throbbing vibrations to the chassis.
A satisfactory compromise between the need to suppress the second, larger-amplitude motions of the engine and the desire to suppress the first, higher-frequency, disturbing, throbbing vibrations is not readily possible because each depends on a different transfer characteristic. The transfer characteristic depends on the arrangement and dimensioning of the structural members of the mount. Modifications therefore require the use of differently arranged and/or sized structural members and, thus, great expense.